Foundry practice



United States Patent 2,779,675 FOUNDRY PRACTICE Gosta Vennerholrn,Dearborn, and Harold N. Bogart, Detroit, Micln, assignors to Ford MotorCompany, Dearborn, Mich, a corporation of Delaware No Drawing.Application June 2., 1953, Serial No. 359,202

9 Claims. (Cl. 75-130) This invention relates to the metallurgicsciences and is more particularly directed to a process for the volumeproduction of low oxygen, low sulphur iron at the lowest possibleover-all cost.

In the course of extensive experimentation and production runs coveringover one hundred thousand tons, we have established that practically allcommercial melting apparatus may be employed to give a base metalsuitable for deoxidizing and desulphurizing outside of the meltinginstrumentality. In this work we have employed the acid electricfurnace, the basic electric furnace, the acid cupola, basic cupola andvarious duplex combinations of the cupola followed by the electricfurnace. In the course of this work it became very apparent that nodulariron could be produced with a much smaller magnesium addition and a muchsmaller magnesium residue i. e., a magnesium residue of 0.005% to0.030%, if the base metal were 'desulphurized and deoxidized to theproper degree prior to the addition of magnesium. Similarly, savings ofother nodularizing agents such as titanium, zirconium, nitrogen, ceriumand their mixtures with each other or magnesium may be obtained. This isin accordance with views held by the art since the commercial productionof nodular iron began. The need for a drastically deoxidizing anddesulphurized iron in large volumes and at low cost indicates primarilyone melting apparatus; that is, a basicly operated cupola.

Attempts to operate in a conventional basic cupola were not acceptable.The results were erratic, and only a slight reduction was made in theamount of nodularizing additive required. The erosion of the cupolarefractory was so severe that it was often impossible to complete theusual sixteen hour cupola campaign. To alleviate this condition theexterior of the cupola shell adjacent the melting zone and well wasarranged to be cooled by directly impinging thereupon a vigorous sprayof water. In place of the ordinary thick refractory basic lining in themelting zone and well, a very thin basic lining was used in the meltingzone and a neutral lining such as carbon used in the well and permittedto reach an equilibrium with the molten slag on the interior of thecupola. In some instances the basic lining may be omitted entirely. Thewater cooling insures preeminently satisfactory service in each casedespite the use of highly corrosive calcareous slags containing largeamounts of floor spar and calcium carbide by which the basic operationof the cupola is efiected.

To obtain a metal consistently low in oxygen and sulphur it has beenfound necessary to change the arrangement of the cupola tuyeres. In theordinary cupola the combustion air is injected into the mass ofincandescent carbon at a point adjacent the wall of the cupola. Thispractice has been found to permit a preferential flow of the air up thecupola in a zone immediately adjacent the comparatively cold refractorywall and hence to permit unreacted oxygen to ascend well up into thecupola. In this way a long vertical oxidizing zone is produced which isinimical to the consistent production of an iron very low in oxygen. Toavoid this difiiculty it has been found necessary to project the tuyeresabout eight to ice twenty inches into the cupola proper past the wallwhen working with a nominally 100 inch cupola. By this expedient all ofthe air must flow through a comparatively long path over incandescentcoke before it can be subjected into the chilling action of therefractory Wall or the descending melt.

In the conventional operation of a basic cupola approximately 5% oflimestone based on the weight of metallics is the usual flux togetherwith suificient fluor spar to insure the necessary liquidity. This fluxcharge has been found inadequate for the production of low oxygen andsulphur metal suitable for conversion to nodular iron. However,satisfactory results have been obtained by the use of a very highlimestone comprising 10% limestone based upon metallics to which isadded 3% of fluor spar and calcium carbide periodically as indicated bymelting conditions. To insure the proper rate of the oxidation atrelatively high coke ratio must be employed. It has been found that a.ratio of slightly more than one part by weight of coke to five ofmetallics is most satisfactory. A typical charging schedule is tabulatedbelow.

Steel, 0-1500 lbs-preferred, 1000 lbs.

Bessemer pig iron, 0-1500 lbs.preferred, 520 lbs.

Returns, 500-2000 lbs-preferred, 1400 lbs.

Limestone, 9-12%-preferred, 10%

Floor spar, 2-5%preferred, 3%

Coke, 575-650 lbs.preferred, 625 lbs.

Calcium carbide, 0-40 lbs. per hr.--added each 1 /2 to 2 hours Blastvolume, 8,000-12,000 C. F. M.--preferred 11,000

lbs.

Blast pressure, 10-30 ounces-preferred, 18.

Even when operating with the very drasticly deoxidizing anddesulphurizing conditions outlined above, it has been found that theresults are often erratic if the cupola is controlled by observation ofthe slag color, consistency and iron oxide content as dictated byconventional practice. The inventors have discovered that the onlyreliable indicator which will consistently indicate low oxygen and lowsulphur metal and hence the susceptibility of the metal being producedto nodularization by magnesium additions, is the manganese oxide contentof the slag. In the range of 0.1% to 0.4% manganese oxide consistentlygood nodular iron can be produced with a minimum of nodularizingadditions and residues. This manganese oxide content is in a slagcontaining 50 to calcium oxide, 5 to 20% magnesium oxide, 3 to 15%aluminum oxide, .5 to 1%% sulphur, .25 to 1.25% iron oxide, 13 to 30%silica and 5 to 20% calcium fluoride. However, if the manganese oxide isallowed to go substantially above four tenths of 1% the presence ofsubstantial quantities of oxygen and/or sulphur is a certainty. Suchiron can only be nodularized by the use of large and costly alloyadditions and the results are at best erratic. This is clearlyillustrated by the following tabulation:

In the above tabulation the second column indicates the weight of 8%magnesium ferrosilicon added to a 2500 lb. ladle. The final tabulationindicates the number of scrapped cranks in a total daily production ofabout 9,000. A study of this chart will disclose that high scrap andhigh manganese oxide are coexistent.

Castings made from nodular iron in which there are sharp changes ofsection are plagued with two closely related defects known as copedefect and graphite flotation; The cope defect comprises inclusion ofcarbon coated magnesium oxide plates which float to the upper or copeportion of the casting and cause mechanical weakness. The second effect,graphite flotation, is caused by the presence of excessive amounts ofsilicon in a high carbon casting. Graphite flotation produces resultssimilar to the cope defect in that the lighter graphite floats to thecope portion of the casting and renders it mechanically weak. Graphiteflotation is controlled by carefully regulating the silicon content ofthe final metal to the absolute minimum sufficient to produce therequisite graphite, pearlite balance.

The occurrence of cope defect may be prevented by the addition to theladle of basic cupola slag analyzing from to by weight of calciumfluoride. This fluoride containing flux at the same time acts as ascouring agent and prevents the accumulation of the oxides of thenodularizing and graphitizing additions in the ladle. Although cupolaflux is preferred for this purpose cost wise, any suitable fluoridebearing material may be used, or resort may be had to commerciallyavailable magnesium type fluxes.

To insure commercially acceptable results it has been found necessary toadd a forehearth to the pouring apparatus to insure a supply of metal ofuniform temperature and chemical analysis despite variations in theoperation of the cupola. In the ordinary practice this forehearth isunfired except to heat it up for the initial reception of metal.

Despite the most meticulous care in the operation of cupola it has beenfound that occasionally the manganese oxide content of the slag willrise beyond the desired upper limit of four tenths of a percent andprompt corrective treatment must be taken if the consumption ofmagnesium alloy and the production of scrap is not be excessive. Thelogical corrective measure would appear to be a decrease in the windvolume and an increase in the rate of coke charging. This has been triedand is successful after a lapse of about the forty minutes which isrequired for the additional coke to descend to the melting zone. Toavoid this undesirably long period of only partial deoxidized metal anaddition of about forty pounds of calcium carbide has been found toeffect an almost immediate reduction in the manganese oxide content ofthe slag thereby preventing the production of excessive amounts ofscrap. The same rapid correction may be obtained by the addition in theblast and through the tuyeres of any readily, available low sulphurcontent fuel. For example, natural gas or coke oven gas or low sulphurfuel oil may be injected through the tuyeres to reestablish the desiredstrongly deoxidizing conditions at the bottom of the cupola. lfsufficicntly sulphur free pulverized coal is at hand it may also beinjected as an alternative to or in conjunction with the fluid fuelsjust mentioned.

We claim as our invention:

1, The process of producing nodular iron castings comprising charginginto a basicly operated cupola a ferrous charge, limestone to the extentof 9 to 12%, fluorspar to the extent of 2 to 5% and coke to the extentof 575 to 650 pounds to each 2920 pounds of metallics, injecting airinto the cupola at a plurality of points which are substantiall removedfrom the wall of the cupola, regulating the blowing rate to produce aniron substantially saturated with carbon and to produce a slag having amanganese oxide content of from 0.1% to 0.4%, tapping the cupola intoladles to which has been added granulated basic cupola slag containing 5to 20% by weight calcium fluoride, adding a magnesium bearing alloy inan amount to leave a magnesium residual of from 0.005% to 0.030%,inoculating and casting the metal.

2. The process of producing nodular iron castings comprising charginginto a basicly operated cupola a ferrous charge, limestone to the extentof 9 to 12%, fluor spar to the extent of 2 to 5% and coke to the extentof 575 to 650 pounds to each 2920 pounds of metallics, injecting airinto the cupola at a plurality of points which are substantially removedfrom the wall of the cupola, regulating the blowing rate to produce aniron substantially saturated with carbon and to produce a slag having amanganese oxide content of from 0.1% to 0.4%, tapping the cupola intoladles to which has been added a fluoride containing flux, adding amagnesium bearing alloy in an amount to leave a magnesium residual offrom 0.005% to 0.030%, inoculating and casting the metal.

3. The process of producing nodular iron castings comprising charginginto a basically operated cupola a ferrous charge, limestone to theextent of 9 to 12%, fluor spar to the extent of 2 to 5% and coke to theextent of 575 to 650 pounds to each 2920 pounds of metallics, injectingair into the cupola at a plurality of points which are substantiallyremoved from the wall of the cupola, regulating the blowing rate toproduce an iron.

substantially saturated with carbon and to produce a slag having amanganese oxide content of from 0.1% to 0.4%, tapping the cupola intoladles to which has been added magnesium ilux, adding a magnesiumbearing alloy in an amount to leave a magnesium residual of from 0.005%to 0.030%, inoculating and casting the metal.

The process of producing nodular iron castings comprising charging intoa basicly operated cupola a fer rous charge, limestone to the extent of9 to 12%, iiuor spar to the extent of 2 to 5% and coke to the extent of575 to 650 pounds to each 2920 pounds of metallics, injecting air intothe cupola at a plurality of points which are substantially removed fromthe wall of the cupola, regulating the blowing rate to produce an ironsubstantially saturated with carbon and to produce a slag having amanganese oxide content of from 0.1% to 0.4%, correcting irregularitiesin the operation of the cupola by the periodic charging of small amountsof calcium carbide, and adding a magnesium bearing alloy in an amount toleave a magnesium residual of from 0.005 to 0.030%.

5. The process of producing nodular iron castings comprising charginginto a basicly operated cupola a ferrous charge, limestone to the extentof 9 to 12%, fiuor spar to the extent of 2 to 5% and coke to the extentof 575 to 650 pounds to each 2920 pounds of metal lics, injecting airinto the cupola at a plurality of points which are substantially removedfrom the wall of the cupola, regulating the blowing rate to produce aniron substantially saturated with carbon and to produce a slag having amanganese oxide content of from 0.1% to 0.4%, correcting irregularitiesin the operation of the cupola by the periodic charging through thetuyeres of small amounts of calcium carbide, and adding a ma,,- nesiumbearing alloy in an amount to leave a magnesium residual of from 0.005%to 0.030%.

6. The process of producing nodular iron castings comprising charginginto a basically operated cupola a ferrous charge, limestone to theextent of 9 to 12%, fiuor spar to the extent of 2 to 5% and cope to theextent of 575 to 650 pounds to each 2920 pounds of metallies, injectingair into the cupola at a plurality of points which are substantiallyremoved from the wall of the cupola, regulating the blowing rate toproduce an iron substantially saturated with carbon and to produce aslag having a manganese oxide content of from 0.1% to 0.4%, correctingirregularities in the operation of the cupola by the periodic chargingthrough the charging door of small amounts of calcium carbide, andadding a magnesium bearing alloy in an amount to leave a magnesiumresidual of from 0.005% to 0.030%.

7. The process of producing nodular iron castings comprising charginginto a basicly operated cupola a ferrous charge, limestone to the extentof 9 to 12%, fluor spar to the extent of 2 to 5% and coke to the extentof 575 to 650 pounds to each 2920 pounds of metallics, injecting airinto the cupola at a plurality of points which are substantially removedfrom the Wall of the cupola, regulating the blowing rate to produce aniron substantially saturated with carbon and to produce a slag having amanganese oxide content of from 0.1% to 0.4%, correcting irregularitiesin the operation of the cupola by the periodic charging of a low sulphurcarbonaceous fuel through the tuyeres, tapping the cupola into ladles towhich has been added a fluoride containing flux, adding a magnesiumbearing alloy in an amount to leave a magnesium residual of from 0.005%to 0.030%, inoculating and casting the metal.

8. The process of producing nodular iron castings comprising charginginto a basicly operated cupola a ferrous charge, limestone to the extentof 9 to 12%, fluor spar to the extent of 2 to 5% and coke to the extentof 575 to 650 pounds to each 2920 pounds of metallics, injecting airinto the cupola at a plurality of points which are substantially removedfrom the wall of the cupola, regulating the blowing rate to produce aniron substantially saturated with carbon and to produce a slag having amanganese oxide content of from 0.1% to 0.4%, cooling the cupola shellat the melting and well level by externally applied streams of water,tapping the cupola into ladles to which has been added a fluoridecontaining flux, adding a magnesium bearing alloy in an amount to leavea magnesium residual of from 0.005% to 0.030%, inoculating and castingthe metal.

9. The process of producing nodular iron castings comprising charginginto a basicly operated cupola a ferrous charge, limestone to the extentof 9 to 12%, rluor spar to the extent of 2 to 5% and coke to the extentof 575 to 650 pounds to each 2920 pounds of metallics, injecting airinto the cupola at a plurality of points which are substantially removedfrom the Wall of the cupola, regulating the blowing rate to produce aniron substantially saturated with carbon and to produce a slag having amanganese oxide content of from 0.1% to 0.4%, tapping the cupola intoladles to which has been added a fluoride containing flux, adding anodularizing alloy sufiicicnt to leave a magnesium residual of from0.005% to 0.030% and casting the metal.

OTHER REFERENCES American Foundryman, August 1949, page 40. Published bythe American Foundrymens Society, Chicago, Illinois.

2. THE PROCESS OF PRODUCING NODULAR IRON CASTINGS COM PRISING CHARGINGINTO A BASICLY OPERATED CUPOLA A FERROUS CHARGE, LIMESTONE TO THE EXTENTOF 9 TO 12%, FLUOR SPAR TO THE EXTENT OF 2 TO 5% AND COKE TO THE EXTENTOF 575 TO 650 POUNDS TO EACH 2920 POUNDS OF METALLICS, INJECTING AIRINTO THE CUPOLA AT A PLURALITY OF POINTS WHICH ARE SUBSTANTIALLY REMOVEDFROM THE WALL OF THE CUPOLA, REGULATING THE BLOWING RATE TO PRODUCE ANIRON SUBSTANTIALLY SATURATED WITH CARBON AND TO PRODUCE A SLAG HAVING AMANGANESE OXIDE CONTENT OF FROM 0.1% TO 0.4%, TRAPPING THE CUPOLA INTOLADLES TO WHICH HAS BEEN ADDED A FLOURIDE CONTAINING FLUX, ADDING AMAGNESIUM BEARING ALLOY IN AN AMOUNT TO LEAVE A MAGNESIUM RESIDUAL OFFROM 0.005% TO 0.030%, INOCULATING AND CASTING THE METAL.